The present invention relates to an information recording/reproducing optical disk which allows to record/reproduce information in units of sectors arranged along a spiral track, and a method of forming the same.
Examples of so-called rewritable optical disks allowing information recording/reproduction, which are already commercially available, are a 120-mm magneto-optical disk, 90-mm magneto-optical disk, and a 120-mm phase change disk (so-called PD).
These disks have guide grooves for guiding laser beam radiation, and tracking is performed using diffraction of a laser beam due to the guide grooves. The guide groove is formed continuously and spirally from the inner peripheral portion to the outer peripheral portion of the disk. This guide groove portion is called a groove, and the remaining portion is called a land. In the conventional optical disk, information is recorded only on one of the groove and land.
Information on such an optical disk is read/written in units of 512 or 2,048 bytes. This information unit is called a sector. Each sector has a sector address representing the address of the sector and is formatted in accordance with a predetermined sector format to record information on a target sector and reliably reproduce the information. Sector address information is recorded by forming recesses called pits at the start of the sector in formatting. The portion where the sector address information is recorded is called a header. In the conventional optical disk, information is recorded only on one of the groove and land, as described above. For this reason, the header is also formed only on the groove in groove recording or only on the land in land recording.
In the conventional optical disk, information is recorded only in one of the groove and land. However, it is readily expected that a larger recording capacity can be realized by recording information on both the land and groove.
However, to record information on both the land and groove, the method of forming sector addresses poses a problem. This problem will be described below.
In the conventional optical disk having a spiral groove, the groove is parallel to the land. The groove and land form spiral loci parallel to each other. Such a conventional optical disk structure will be referred to as a double spiral structure hereinafter.
In this double spiral structure, the groove and land are parallel, so movement from the groove to the land always requires a track jump. When information recording/reproduction is switched from the groove to the land (or from the land to the groove), a track jump or seek is required, so continuous information recording/reproduction is difficult.
In addition, when the disk having the double spiral structure is to be formatted, sectors on the groove (to be referred to as groove sectors hereinafter) and sectors on the land (to be referred to as land sectors hereinafter) must be independently formatted. This is disadvantageous in formatting the disk such that information can be alternately recorded/reproduced on/from the land and groove adjacent to each other by a zone CAV (constant angular velocity) scheme.
More specifically, to form continuous sector addresses on the land and groove adjacent to the land, only the groove or only the land must be formatted while assigning intermittent addresses in units of tracks. In this case, it is difficult to format the disk such that the address positions match at the connection portion where the addresses are continuously assigned from the land to the groove or from the groove to the land. In addition, if movement from the land to the groove or from the groove to the land in recording/reproducing information is not smooth, a wait for disk rotation occurs, so continuous information recording/reproduction is inhibited.
The present invention has been made to solve the above problems, and has as its object to provide an information recording/reproducing optical disk and a method for forming the same having a large recording capacity and allowing continuous information recording/reproduction with high reliability.